The invention relates to an integral rocket and ramjet engine of the type suitable for use in a missile.
A missile ramjet engine operates by aerodynamically compressing air in an intake duct, burning fuel in a combustion chamber, the combustion being supported by the compressed air and then ejecting the resultant hot gases through a propelling nozzle in which the hot gases expand thereby attaining a high velocity rearward relative to the direction of the missile.
It is known to use a detachable rocket engine to accelerate the missile up to high speed in order to sufficiently compress air in the intake duct to commence operation of the ramjet. After the missile reaches a high enough velocity for the ramjet to be self-sustaining the rocket engine is discarded.
To save space and weight, it is also known to provide a rocket grain within the ramjet combustion chamber for initial acceleration of the missile. The integral rocket and ramjet engine has drawbacks such as the propelling nozzle size needs to change when the engine converts from a rocket to a ramjet. Also, during the period in which the rocket charge burns it is necessary to seal off the air intake from the combustion chamber to prevent efflux from the rocket charge travelling via the intake duct to atmosphere. The means used to seal off the air intake needs to be able to withstand the very high gas pressure generated by the burning charge as well.
The former drawback has largely been overcome by housing the rocket nozzle within the ramjet nozzle and during transition from rocket to ramjet operation ejecting the rocket nozzle from the missile by various known means. Another solution is to burn away the rocket nozzle during transition.
The latter drawback hitherto has been overcome by having one or more covers between the air intake duct and combustion chamber which are ejected from the missile during transition by convenient means. Jettisoning the covers creates two main problems. First, the ejected covers become a hazard, especially to aircraft in the case of an air launched missile. Secondly, after the covers have been jettisoned there will invariably be some form of sudden enlargement between the intake duct and combustion chamber which is used as a pilot combustion region. This feature involves a higher than desirable pressure loss, only overcome by increasing the size of the engine.
The present invention seeks to provide an integral rocket and ramjet engine which does not suffer from the problems described in the preceding paragraph.
The integral rocket and ramjet engine, as claimed, is provided with a port cover which seals the intake duct from the combustion chamber while the engine operates as a rocket and overcomes problems associated with ejecting the cover by retaining it within the combustion chamber when the engine operates as ramjet, the cover providing a quiet zone which is shielded from the main flow of air into the combustion chamber. Preferably combustion equipment such as fuel manifolds and flame gutters are attached to the cover and become operational when the cover takes up its new position after change-over from rocket to ramjet mode.